1. Field of the Invention
The present invention relates to a method and apparatus for spraying an inorganic hydraulic material composition containing reinforcing short fibers. More particularly, the present invention relates to a method and apparatus for spraying an inorganic hydraulic material composition in which reinforcing short fibers are uniformly distributed without breakage and intertwinement of the fibers.
2. Description of the Related Art
Various known methods and apparatuses for spraying an aqueous slurry containing an inorganic hydraulic material such as a cement, an aggregate such as sand, and reinforcing short fibers such as glass or metal fibers are utilized in the civil engineering, construction, and building industries.
In the known methods and apparatus, the inorganic hydraulic material and the aggregate are mixed with the reinforcing short fibers in water, and the resultant aqueous slurry is sprayed through a spraying nozzle.
Usually, the reinforcing short fibers are prepared by cutting a fibrous bundle of a number of filaments to a desired length. Therefore, the reinforcing short fibers are usually supplied in the form of bundles of short cut fibers which are parallel to each other.
It is well known that it is very difficult to release the short fibers from the bundles and to evenly disperse and distribute the released short fibers in water. That is, it is very difficult to prepare an aqueous slurry of the inorganic hydraulic material wherein the reinforcing short fibers are uniformly dispersed and evenly distributed. When an aqueous slurry in which the reinforcing short fibers are unevenly mixed with the inorganic hydraulic material in water is sprayed and allowed to harden (solidify), the resultant hardened structure exhibits an unsatisfactory mechanical strength. Therefore, the individual short fibers must be completely released from the bundles and the released individual short fibers evenly mixed with the inorganic hydraulic material.
Accordingly, to ensure a complete release of the individual short fibers from the bundles and a uniform dispersal of the released individual short fibers in water, a specific exclusive mixer, for example, an OMNI type mixer, must be used.
This necessity for a specific exclusive mixer greatly restricts the scope of application of the aqueous slurry containing the reinforcing short fibers in the civil engineering, construction and building industries. Also, the mixing by the specific exclusive mixer results in undesirable breakage, intertwinement, and/or fibrillation of the reinforcing short fibers. Further, mixing in water promotes an undesirable absorption of water by the reinforcing short fibers, which have a relatively large surface area, and this water absorption sometimes promotes an undesirable deterioration of the reinforcing short fibers, resulting in a decrease in the toughness of the short fibers. Accordingly, a satisfactory reinforcing effect of the short fibers cannot be obtained from an aqueous slurry of the inorganic hydraulic material in which the reinforcing short fibers are dispersed by the specific exclusive mixer.
Furthermore, when an aqueous slurry of the inorganic hydraulic material containing the reinforcing short fibers, for example, short metal fibers, is sprayed onto a surface of a wall, the distribution of the inorganic hydraulic material and the reinforcing short fibers in the resultant aqueous slurry layer on the wall surface is uneven because of the difference in specific gravity thereof. That is, the metal fibers have a large specific gravity and strongly rebound from the wall surface, and therefore, the distribution of the reinforcing short metal fibers in a portion of the hardened layer closest to the wall surface is smaller than that in a surface portion thereof furthest from the wall surface. This results in an unsatisfactory reinforcing effect of the short fibers in the hardened layer, and the metal fibers located in the surface portion of the hardened layer are easily corroded by corrosive gases, for example, oxygen, moisture, and/or a corrosive mist, for example, salt mist.
Taking the above-mentioned circumstances into account, there is a strong demand for a new method and apparatus by which the inorganic hydraulic material can be evenly mixed with the reinforcing short fibers and can produce a uniform spray of the resultant evenly mixed composition of the inorganic hydraulic material and the reinforcing short fibers.